Installation instruction for Rockbox on iBasso DX50

prerequisites: Any stock firmware. If you have an older rockbox installation with cwm, follow first the violet reverting instruction below

Download the files:
a) plain Firmware 1.6.0 including the rockbox dualboot app: download form sendspace
b) the latest rockbox build from the official page (it is a development build but problems are rare):

connect your player to the computer to have access to the internal and external storage

copy the update.img to the root of your microSD card (from the DX50Firmware_V1.6.0_with_rockbox_bl_20150225.zip)

extract the content of the rockbox-build-zip to the internal drive of your DX50 (it contains a single folder ".rockbox"). If the file browser asks questions about merging and overwriting an older rockbox installation, confirm them with "yes", "overwrite" or "merge"

reboot to recovery: Power off the device, then power it on the device while you are holding vol+

2. Connect your player to the computer and open the internal memory (usual name: DX50). There should be a folder "rockbox", open it

3. Open the downloaded theme zip file. In the zip file there is a folder named ".rockbox" (yes, with a dot)

4. Open the ".rockbox" folder in your theme-zip and extract all the content to your "rockbox" folder on your player
you're done, now you can select your new theme in Settings -> Theme Settings -> Browse Theme Files

/sdcard is the partition on the embedded MMC that is exposed over USB. It's what we typically refer to as the internal storage on the device. This is a legacy of the early days of Android where a uSD card slot was part of the hardware specifications and a microSD card was necessary just to use the OS. When Google eased the uSD requirements they chose to use a chunk of eMMC as the /sdcard file system to maintain backwards compatibility with older applications.

Removable cards are usually mounted as /mnt/ext_sdcard or something similar. DX50 uses the /mnt/ext_sdcard mount point.

Rockbox plays anything but downsamples to 16/48 before sending it to the dac as I understand it

Correct. And then the DAC oversamples so that most aliasing artifacts are pushed above 20 kHz where they're inaudible, and then it uses a low pass filter at 20 kHz to cut those artifacts off. All that a 192 kHz file does is skip the oversampling step. You still get the 20 kHz low pass filter to remove high frequency artifacts. That's why nobody has bothered implementing so-called high resolution playback in Rockbox. It's just going to be cut off by the DAC. This includes the Wolfson WM8740 chip in DX50. You can read Wolfson's own spec sheet here:

Citing note 2 on page 7:2. All performance measurements done with 20kHz low pass filter. Failure to use such a filter will result in higher THD+N and lower SNR and Dynamic Range readings than are found in the Electrical Characteristics. The low pass filter removes out of band noise; although it is not audible it may affect dynamic specification values.